More Spirit Warriors by a Necromancer (Serpent clan)
Train 4 Ronins and bring them to the Necromancer Throne. A Necromancer will appear. Summon three Spirit Warriors and then quick save the game. Now bring those three Spirit Warriors to fight and let them die. Then, quick load the game and you will now be able to summon three new Spirit Warriors with a same Necromancer. The three newly summoned Spirit Warriors must go to die, then quick save the game. Repeat the steps to summon more Spirit warriors.